Magnetoresistive head and the fabricating method

ABSTRACT

There is provided a magnetoresistive head which can realize high sensitivity and low noise even when the reading track is being reduced. Longitudinal biasing is performed to a ferromagnetic free layer whose magnetization is rotated according to an external magnetic field by providing unidirectional magnetic anisotropy by exchange coupling to an antiferromagnetic layer. A hard magnetic film is arranged at the edge of a magnetoresistive film to reduce an effective reading track width.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetoresistive head which readsinformation written onto a magnetic recording medium, and morespecifically to a magnetoresistive head of a novel longitudinal biasingmethod of a ferromagnetic layer for detecting a signal field and thefabricating method.

2. Description of the Related Art

In a magnetoresistive head mounted as a reading element on a magneticrecording and reading device, a GMR (Giant Magnetoresistive) head usinga spin valve film having a basic structure of ferromagnetic freelayer/nonmagnetic conductive layer/ferromagnetic film fixinglayer/antiferromagnetic layer described in Japanese Published UnexaminedPatent Application No. Hei 4-358310 is widely used at present. In themagnetoresistive head, in order to inhibit Barkhausen noise,longitudinal biasing must be performed to a ferromagnetic free layerwhose magnetization direction is changed by a signal field. As thelongitudinal biasing method, Japanese Published Unexamined PatentApplication No. Hei 7-57223 describes a method in which a hard magneticfilm or a deposited film of a ferromagnetic film and anantiferromagnetic film is arranged at each edge of a magnetoresistivefilm to set a ferromagnetic free layer on single domain state. Theformer is called a hard biasing structure which is the mainstream of thecurrent head structure.

The hard biasing structure applies a longitudinal biasing field to aferromagnetic free layer and is effective for inhibiting Barkhausennoise. On the other hand, it is widely known that magnetization at theedge of an element is fixed to form the so-called insensitive zone.Since the magnetization direction in the insensitive zone is not changedby a signal field, formation of the insensitive zone substantiallyreduces the reading sensitivity. With the future increase of the surfacerecording density of a magnetic recording and reading device, the trackwidth is being reduced to increase the occupying percentage of theinsensitive zone. This problem is expected to be significant.

To reduce formation of the insensitive zone for the purpose of ensuringthe reading sensitivity, the film thickness of a hard magnetic film isdecreased to reduce a longitudinal biasing field applied to theferromagnetic free layer. The effect for inhibiting Barkhausen noise isinsufficient. This means that inhibition of Barkhausen noise andreduction of insensitive zone formation are in a trade-off relationwhich is difficult to satisfy both.

As another means for performing-longitudinal biasing to a ferromagneticfree layer, Japanese Published Unexamined Patent Application No.2000-173020 describes a longitudinal biasing structure by interfaceexchange coupling. Since this structure exchange couples the entiresurface of a ferromagnetic free layer to an antiferromagnetic layer, ithas a reliable and uniform longitudinal biasing effect. In the hardbiasing structure previously described, the geometrical arrangementrelation between a hard magnetic film and a ferromagnetic free layer andthe shape of an element by patterning affect the magnitude of thelongitudinal biasing field. On the contrary, in the longitudinal biasingstructure by interface exchange coupling, antiferromagnetic material andits film thickness are selected and a suitable exchange coupling fieldbiasing layer is interposed between a ferromagnetic free layer and anantiferromagnetic layer. An advantage of easily adjusting a longitudinalbiasing field can be expected. Since an insensitive zone is not formedat the edge of the ferromagnetic free layer, an effective reading trackwidth is increased whereby adaptability to the future track reduction isfeared. In addition, since a magnetic pole is caused at the edge of theferromagnetic free layer, magnetization of the edge is expected to beunstable. A sufficient longitudinal biasing effect cannot be obtained.The influence of this is expected to be significant as the geometricaltrack width is being reduced.

SUMMARY OF THE INVENTION

In consideration of the future increase of the surface recording densityof a magnetic recording and reading device, as described above, it canbe expected that it is difficult to realize both inhibition ofBarkhausen noise and ensuring of the reading sensitivity in the hardbiasing structure, and reduction of the reading track width in thelongitudinal biasing structure by interface exchange coupling. The priorart longitudinal biasing means cannot obtain reading characteristicwhich can correspond to the future magnetic recording and reading devicewith a high recording density and imposes an important problem ofestablishment of novel longitudinal biasing means. This is not limitedto the current CIP (Current in the plane)-GMR head, but is a commonproblem for a CPP (Current perpendicular to the plane)-GMR head and aTMR (Tunneling Magnetoresistive) head which are expected to be practicalas the next generation head.

Accordingly, an object of the present invention is to provide amagnetoresistive head which applies longitudinal biasing meanssatisfying all of inhibition of Barkhausen noise, high readingsensitivity, and reduction of an effective reading track width and thefabricating method.

To achieve the foregoing object, in the present invention, amagnetoresistive head having a first and a second ferromagnetic layersseparated by a nonmagnetic conductive layer or a nonmagnetic tunnelingbarrier layer; a magnetoresistive film in which the magnetizationdirection of the first ferromagnetic layer is fixed by a firstantiferromagnetic layer provided to be contacted with the firstferromagnetic layer opposite to the nonmagnetic conductive layer or thenonmagnetic tunneling barrier layer; and a pair of electrodes forflowing a sense current to the magnetoresistive film, includes: a secondantiferromagnetic layer arranged so as to provide unidirectionalmagnetic anisotropy to the second ferromagnetic layer; and a hardmagnetic film arranged so as to apply a magnetic field to the secondferromagnetic layer.

In the present invention, a second antiferromagnetic layer is formed tobe contacted with the second ferromagnetic layer opposite to thenonmagnetic conductive layer or the nonmagnetic tunneling barrier layer,and a hard magnetic film is formed at each edge of the magnetoresistivefilm in the track width direction.

In the present invention, a magnetoresistive head having a first and asecond ferromagnetic layers separated by a nonmagnetic conductive layeror a nonmagnetic tunneling barrier layer; a magnetoresistive film inwhich the magnetization direction of the first ferromagnetic layer isfixed by a first antiferromagnetic layer provided to be contacted withthe first ferromagnetic layer opposite to the nonmagnetic conductivelayer or the nonmagnetic tunneling barrier layer; a magnetic flux guidefor guiding an external magnetic field to the second ferromagneticlayer; and a pair of electrodes for flowing a sense current to themagnetoresistive film, includes: a second antiferromagnetic layerarranged so as to provide unidirectional magnetic anisotropy to thesecond ferromagnetic layer; a third antiferromagnetic layer arranged soas to provide unidirectional magnetic anisotropy to the magnetic fluxguide; and a hard magnetic film arranged so as to apply a magnetic fieldto the second ferromagnetic layer and the magnetic flux guide.

A second antiferromagnetic layer is formed to be contacted with thesecond ferromagnetic layer opposite to the nonmagnetic conductive layeror the nonmagnetic tunneling barrier layer, a third antiferromagneticlayer is formed to be contacted with the magnetic flux guide, and a hardmagnetic film is formed at each edge of the magnetoresistive film in thetrack width direction and at each edge of the magnetic flux guide in thetrack width direction.

The direction of unidirectional magnetic anisotropy provided to thesecond ferromagnetic layer by the second antiferromagnetic layer -or thedirection of unidirectional magnetic anisotropy provided to the magneticflux guide by the third antiferromagnetic layer, and the direction of amagnetic field applied to the second ferromagnetic layer or the magneticflux guide from the hard magnetic film are roughly matched.

The direction of unidirectional magnetic anisotropy provided to thefirst ferromagnetic layer by the first antiferromagnetic layer and thedirection of unidirectional magnetic anisotropy provided to the secondferromagnetic layer by the second antiferromagnetic layer or thedirection of unidirectional magnetic anisotropy provided to the magneticflux guide by the third antiferromagnetic layer are roughly orthogonal,and when temperatures at which unidirectional magnetic anisotropydisappears (blocking temperatures) in the first antiferromagnetic layer,the second antiferromagnetic layer and the third antiferromagnetic layerare T_(B1), T_(B2) and T_(B3), T_(B1)>T_(B2)=T_(B3).

When a saturation flux density of the second ferromagnetic layer isB_(S2), its film thickness is t₂, a remaining flux density of the hardmagnetic film is Br_(h), and its film thickness is t_(h), a longitudinalbiasing ratio defined by Br_(h)·t_(h)/B_(S2)·t₂ is below 4.

A nonmagnetic layer is interposed between the second ferromagnetic layerand the second antiferromagnetic layer.

The first antiferromagnetic layer is made of an ordered alloyantiferromagnetic film expressed by Mn−M₁ in which M₁ is composed of atleast one or more elements of Ni, Ru, Rh, Pd, Ir and Pt, and the secondantiferromagnetic layer is made of a disordered alloy antiferromagneticfilm expressed by Mn−M₂ in which M₂ is composed of at least one or moreelements of Cr, Fe, Ru, Rh, Pd, Ir and Pt.

Further, in the present invention, a method for fabricating amagnetoresistive head including depositing a first and a secondferromagnetic layers via a nonmagnetic conductive layer or a nonmagnetictunneling barrier layer; providing a first antiferromagnetic layeropposite to the nonmagnetic conductive layer or the nonmagnetictunneling barrier layer to form a magnetoresistive film; forming a pairof electrodes for flowing a sense current to the magnetoresistive film;arranging a second antiferromagnetic layer so as to provideunidirectional magnetic anisotropy to the second ferromagnetic layer;arranging a hard magnetic film so as to apply a magnetic field to thesecond ferromagnetic layer; arranging a magnetic flux guide for guidingan external magnetic field to the second antiferromagnetic layer; andarranging a third antiferromagnetic layer so as to provideunidirectional magnetic anisotropy to the magnetic flux guide, includesa process for finally deciding by the direction of a magnetic fieldapplied at annealing the direction of unidirectional magnetic anisotropyprovided to the first ferromagnetic layer by the first antiferromagneticlayer and the direction of unidirectional magnetic anisotropy providedto the second ferromagnetic layer or the magnetic flux guide by thesecond antiferromagnetic layer, wherein the process subjects the firstantiferromagnetic layer, the second antiferromagnetic layer or the thirdantiferromagnetic layer to annealing in the magnetic field underconditions of a temperature set from high to low in order of decreasingblocking temperature so as to provide the unidirectional magneticanisotropy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a first embodiment of amagnetoresistive head of the present invention;

FIG. 2 is a schematic sectional view of a second embodiment of amagnetoresistive head of the present invention;

FIG. 3 shows schematic plan and sectional views of a third embodiment ofa magnetoresistive head of the present invention;

FIG. 4 is a diagram showing annealing temperature dependence of anexchange coupling field provided by a MnPt film;

FIG. 5 is a diagram showing annealing temperature dependence of anexchange coupling field provided by a MnIr film;

FIG. 6 is a diagram showing temperature dependence of an exchangecoupling field provided by a MnPt film and an MnIr film;

FIG. 7 is a diagram showing micro track characteristic of a prior artmagnetoresistive head structure;

FIG. 8 is a diagram showing micro track characteristic of amagnetoresistive head structure of the present invention; and

FIG. 9 is a diagram showing micro track characteristic of amagnetoresistive head structure of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detailhereinbelow with reference to the drawings.

FIG. 1 shows a cross-sectional view of a magnetoresistive head of afirst embodiment of the present invention. An overview of a headfabricating procedure will be described hereinbelow. After forming alower shield 110 and a lower gap 120 on a substrate 100, amagnetoresistive film 130 is deposited and is patterned into a desiredshape using photolithography and ion milling. A hard magnetic film 140and an electrode 150 are formed at each edge of the magnetoresistivefilm 130 using a lift-off method. An upper gap 160 and an upper shield170 are formed. The detailed film structure of the magnetoresistive film130 includes underlayer 131/first antiferromagnetic layer 132/firstferromagnetic layer 133/nonmagnetic conductive layer 134/secondferromagnetic layer 135/second antiferromagnetic layer 136/protectivelayer 137. The first ferromagnetic layer 133 corresponds to theso-called fixing layer and the second ferromagnetic layer 135corresponds to the so-called free layer. The first antiferromagneticlayer 132 is used for fixing the magnetization direction of the firstferromagnetic layer 133 (fixing layer) in one direction. The secondantiferromagnetic layer 136 only applies a relatively small longitudinalbiasing field to the second ferromagnetic layer 135 (free layer). Themagnetization direction of the second ferromagnetic layer 135 is easilyrotated by an external magnetic field. The relative angles of the firstferromagnetic layer 133 and the second ferromagnetic layer 135 aredifferent by the signal field from a magnetic recording medium. Theelectric resistance of the magnetoresistive film 130 is changedcorresponding to this so as to obtain an electromagnetically-convertednormalized signal output. The longitudinal biasing field applied to thesecond ferromagnetic layer 135 (free layer) by the secondantiferromagnetic layer 136 is set to a suitable value. By this setting,both sufficient inhibition of Barkhausen noise and high readingsensitivity can be provided. Arrangement of the hard magnetic film 140can prevent a magnetic pole from being caused at the edge of theferromagnetic free layer to reinforce the effect for inhibitingBarkhausen noise. The magnitude of a magnetostatic field given from thehard magnetic film 140 does not function to the center region of thesecond ferromagnetic layer 135 (free layer) and remains to the degree offorming a suitable insensitive zone at the edge of the secondferromagnetic layer 135 (free layer) so as to reduce an effectivereading track width without deteriorating the reading sensitivity. Hereis shown an example of the magnetoresistive film 130 to deposite thefirst ferromagnetic layer 133 on the side closer to the substrate 100.The deposition order may be reversed and be underlayer 131/secondantiferromagnetic layer 136/second ferromagnetic layer 135/nonmagneticconductive layer 134/first ferromagnetic layer 133/firstantiferromagnetic layer 132/protective layer 137. The firstferromagnetic layer 133 and the second ferromagnetic layer 135 ascomponents of the magnetoresistive film 130 may be of a single-layerfilm of NiFe or CoFe, a ferromagnetic multi-layer film of CoFe/NiFe, orthe so-called synthetic ferri structure of CoFe/Ru/CoFe. The CIP-GMRhead is described here. The structures of CPP-GMR and TMR heads will bedescribed hereinbelow.

FIG. 2 shows a cross-sectional view of a magnetoresistive head of asecond embodiment of the present invention. An overview of a headfabricating procedure will be described hereinbelow. After forming alower electrode 210 serving as a lower shield on a substrate 200, amagnetoresistive film 220 is deposited and is patterned into a desiredshape using photolithography and ion milling. A structure of firstprotective insulating film 230/hard magnetic film 240/second protectiveinsulating film 250 is formed at each edge of the magnetoresistive film220 using a lift-off method. An upper electrode 260 serving as an uppershield is formed. The detailed film structure of the magnetoresistivefilm 220 includes: (1) in a GMR head, underlayer 221/firstantiferromagnetic layer 222/first ferromagnetic layer 223/nonmagneticconductive layer 224/second ferromagnetic layer 226/secondantiferromagnetic layer 227/protective layer 228; and (2) in a TMR head,underlayer 221/first antiferromagnetic layer 222/first ferromagneticlayer 223/tunneling barrier layer 225/second ferromagnetic layer226/second antiferromagnetic layer 227/protective layer 228. The firstferromagnetic layer 223 corresponds to the so-called fixing layer andthe second ferromagnetic layer 226 corresponds to the so-called freelayer. The first antiferromagnetic layer 222 is used for fixing themagnetization direction of the first ferromagnetic layer 223 (fixinglayer) in one direction. The second antiferromagnetic layer 227 onlyapplies a relatively small longitudinal biasing field to the secondferromagnetic layer 226 (free layer). The magnetization direction of thesecond ferromagnetic layer 226 is easily rotated by an external magneticfield. The relative angles of the first ferromagnetic layer 223 and thesecond ferromagnetic layer 226 are different by the signal field from amagnetic recording medium. The electric resistance of themagnetoresistive film 220 is changed corresponding to this so as toobtain an electromagnetically-converted normalized signal output. Thelongitudinal biasing field applied to the second ferromagnetic layer 226(free layer) by the second antiferromagnetic layer 227 is set to asuitable value. By this setting, both sufficient inhibition ofBarkhausen noise and high reading sensitivity can be provided.Arrangement of the hard magnetic film 240 can prevent a magnetic polefrom being caused at the edge of the ferromagnetic free layer toreinforce the effect for inhibiting Barkhausen noise. The magnitude ofthe magnetostatic field given from the hard magnetic film 240 does notfunction to the center region of the second ferromagnetic layer 226(free layer) and remains to the degree of forming a suitable insensitivezone at the edge of the second ferromagnetic layer 226 (free layer) soas to reduce an effective reading track width without deteriorating thereading sensitivity.

The upper and lower sides of the hard magnetic film 240 are coated withthe first protective insulating film 230 and the second protectiveinsulating film 250. This is because the lower electrode 210 serving asthe lower shield and the upper electrode 260 as the upper shield areprevented from being short-circuited. The second protective insulatingfilm 250 may not be formed. Like substrate/lower shield/lower gap/lowerelectrode/magnetoresistive film, the lower shield and the lowerelectrode may be separately formed, which is the same for the uppershield and the upper electrode. Here is shown an example of themagnetoresistive film 220 to laminate the first ferromagnetic layer 223on the side closer to the substrate 200. The lamination order may bereversed and be underlayer 221/second antiferromagnetic layer 227/secondferromagnetic layer 226/nonmagnetic conductive layer 224/firstferromagnetic layer 223/first antiferromagnetic layer 222/protectivelayer 228, or underlayer 221/second antiferromagnetic layer 227/secondferromagnetic layer 226/tunneling barrier layer 225/first ferromagneticlayer 223/first antiferromagnetic layer 222/protective layer 228.. Thefirst ferromagnetic layer 223 and the second ferromagnetic layer 225 ascomponents of the magnetoresistive film 220 may be of a single-layerfilm of NiFe or CoFe and a ferromagnetic multi-layer film of CoFe/NiFe,or of the so-called synthetic ferri structure of CoFe/Ru/CoFe.

In a magnetoresistive head using a magnetic flux guide not exposing amagnetoresistive film from an ABS (air bearing surface), longitudinalbiasing of the magnetic flux guide is required separately. FIG. 3 showsa plan view and a cross-sectional view viewed from the upper side of thesubstrate surface of the magnetoresistive head according to a thirdembodiment of the present invention. Here is shown the case of employinga TMR film as the magnetoresistive film. An overview of a headfabricating procedure will be described hereinbelow. After forming alower electrode 310 serving as a lower shield on a substrate 300, amagnetoresistive film 320 is deposited and is patterned into a desiredshape using photolithography and ion milling. A structure of thirdprotective insulating film 330/magnetic flux guide 340/thirdantiferromagnetic layer 350 is formed and is patterned likewise.

A structure of first protective insulating film 360/hard magnetic film370/second protective insulating film 380 is formed at each edge of themagnetoresistive film 320 and the structure of third protectiveinsulating film 330/magnetic flux guide 340/third antiferromagneticlayer 350 using a lift-off method. An upper electrode 390 serving as anupper shield is formed. The detailed film structure of themagnetoresistive film 320 is similar to the structure shown in FIG. 2and includes underlayer 321/first antiferromagnetic layer 322/firstferromagnetic layer 323/tunneling barrier layer 325/second ferromagneticlayer 326/second antiferromagnetic layer 327/protective layer 328. Thethird antiferromagnetic layer 350 only applies a relatively smalllongitudinal field to the magnetic flux guide 340. The magnetizationdirection of the magnetic flux guide 340 is easily rotated by anexternal magnetic field. In the head structure, the magnetic flux guide340 is exposed from the ABS. The magnetization of the magnetic fluxguide 340 is rotated by the signal field from a magnetic recordingmedium. The relative angles of the first ferromagnetic layer 323 and thesecond ferromagnetic layer 326 are different corresponding to this. Theelectric resistance of the magnetoresistive film 320 is changedcorresponding to this so as to obtain an electromagnetically-convertednormalized signal output. The reason why the third protective insulatingfilm 330 is formed is that the heights of the magnetic flux guide 340and the second ferromagnetic layer 326 (free layer) are matched.

Although not shown here, a protective layer may be formed on the thirdantiferromagnetic layer 350 as needed. Important is that the firstferromagnetic layer 323 (fixing layer) and the second ferromagneticlayer 326 (free layer) are prevented from being short-circuited by themagnetic flux guide 340 or the third antiferromagnetic layer 350. Asdescribed in the structure of FIG. 2, the second protective insulatingfilm 380 may not be formed. Like substrate/lower shield/lower gap/lowerelectrode/magnetoresistive film, the lower shield and the lowerelectrode may be separately formed, which is the same for the uppershield and the upper electrode. Here is shown an example of themagnetoresistive film 320 to doposit the first ferromagnetic layer 323on the side closer to the substrate 300. The deposition order may bereversed and be underlayer 321/second antiferromagnetic layer 327/secondferromagnetic layer 326/tunneling barrier layer 325/first ferromagneticlayer 323/first antiferromagnetic layer 322/protective layer 328.

In this case, the third protective insulating film 330/magnetic fluxguide 340/the third antiferromagnetic layer 350 need not be formed in aprocess separately from the magnetoresistive film 320. The secondantiferromagnetic layer 327 may serve as the third antiferromagneticlayer 350 and the second ferromagnetic layer 326 may serve as themagnetic flux guide 340. This can be realized by dividing the patterningprocess of the magnetoresistive film 320 into two processes ofprocessing to the underlayer 321 as the lowest surface and processing tothe tunneling barrier layer 325. The first ferromagnetic layer 323 andthe second ferromagnetic layer 325 as components of the magnetoresistivefilm 320 may be a single-layer film of NiFe or CoFe, a ferromagneticmulti-layer film of CoFe/NiFe; or the so-called synthetic ferristructure of CoFe/Ru/CoFe. The magnetoresistive head using a magneticflux guide employing a TMR film as the magnetoresistive film isdescribed above, which is the same for CIP-GMR and CPP-GMR, and thedescription thereof is omitted.

The respective components of the magnetoresistive head shown in FIGS. 1to 3 will be described in detail.

Since the substrate, shield, gap, hard magnetic film, and electrode neednot be particularly limited in the present invention, materialstypically used are described by way of example. Desirable are asubstrate of AlTiC, SiC or Al₂O₃ coated thereon; a shield of asingle-layer or a multi-layer film of an NiFe alloy and a nitridethereof, or a CoZr, CoHf or CoTa amorphous alloy; a gap of Al₂O₃, AlN,SiO₂ and a mixture thereof; a hard magnetic film of a CoPt alloy or Ptor ZrO2 added thereto; and an electrode of Cr, α-Ta or Au.

It is desirable to use a magnetic flux guide of a material having a highpermeability made of a single-layer or a multi-layer film of an NiFealloy and a nitride thereof, or a CoZr, CoHf or CoTa amorphous alloy.

One example of the film structure of the magnetoresistive film will beshown below. The value in ( ) indicates a film thickness and the unit isnm. As a GMR film,Ta(1)/NiFe(2)/MnPt(12)/CoFe(1.5)/Ru(0.8)/CoFe(2)/Cu(2.1)/CoFe(1)/NiFe(2)/MnIr(8)/Ta(1)are preferable. As a TMR film,Ta(1)/NiFe(2)/MnPt(12)/CoFe(1.5)/Ru(0.8)/CoFe(2)/Al(0.5)oxidation/CoFe(1)/NiFe(2)/MnIr(8)/Ta(1)are preferable. From the viewpoint of controllability and massproduction efficiency, these are preferably fabricated by a sputteringmethod. For the ferromagnetic layer, a material composed mainly of Fe,Co and Ni having a high spin polarizability in Fermi energy is used soas to increase the resistive change rate of the magnetoresistive filmacting largely on normalized signal output. The composition and filmthickness are desirably adjusted as needed to ensure, in addition to theresistive change rate, small magnetostriction, low coercivity, a largecoupling magnetic field provided from the antiferromagnetic layer, andsymmetry of the reading waveform. For a nonmagnetic conductive layer inthe GMR film, in addition to Cu, Ag and Au may be used. The tunnelingbarrier layer in the TMR film is formed using the so-called naturaloxidation method which introduces oxygen into a chamber after depositingthe Al film. Al, Si, Ta or Mg may be deposited to form an oxide and anitride, or Al₂O₃, AlN, SiO₂, SiN, Ta₂O₅ or MgO may be directlydeposited.

An ordered alloy MnPt film is used as the first antiferromagnetic layerwhich fixes the magnetization direction of the first ferromagnetic layer(fixing layer) in one direction. An ordered antiferromagnetic filmexpressed by Mn−M₁ may be also used: M₁ is composed of an elementincluding at least one or more Ni, Ru, Rh, Pd, Ir, and Pt. A disorderedMnIr film is used as the second antiferromagnetic layer which applies arelatively small longitudinal biasing field to the second ferromagneticlayer (free layer). Another candidate is made of a material made of adisordered alloy antiferromagnetic film expressed by Mn−M₂ and amaterial of M₂ composed of at least one or more elements of Cr, Fe, Ru,Rh, Pd, Ir and Pt may be used.

To obtain good reading characteristic, in a state that an externalmagnetic field is not applied, the magnetization direction of the firstferromagnetic layer (fixing layer) must be directed in the perpendiculardirection (hereinafter, referred to as the element height direction) tothe ABS and the magnetization direction of the second ferromagneticlayer (free layer) must be directed in the track direction of a magneticrecording medium. These can be realized by providing unidirectionalmagnetic anisotropy by exchange coupling to the first and secondantiferromagnetic layers. The detailed description to realize this willbe done based on the following experimental results.

FIG. 4 shows annealing temperature dependence of an exchange couplingfield H_(ua) in a structure including glass substrate/Ta(5)/Mn₄₈Pt₅₂(15,20, 30)/Co₉₀Fe₁₀(2)/Cu(2.1)/Co₉₀Fe₁₀(1)/Ni₈₅Fe₁₅(3)/Ta(3)(film thicknessunit: nm). Annealing is conducted in a vacuum below 1×10⁻³ Pa whileapplying a magnetic field of 240 kA/m in one direction and holding timeis three hours. Although not shown in the drawing, H_(ua) is notexhibited immediately after deposition. Immediately after deposition,the MnPt film is not of an ordered CuAuI type structure showingantiferromagnetism, but is of a disordered fcc structure. This isunderstood to show paramagnetism. To obtain a sufficiently large H_(ua)in applying the magnetic head, annealing at 230 to 270° C. is needed. Asthe annealing temperature is higher, the H_(ua) is increased. When theannealing temperature is raised above 300° C., the resistive change rateis lowered and the interlayer coupling field functioning between thefree layer and the fixing layer is increased. It is not preferable.

FIG. 5 shows annealing temperature dependence of an exchange couplingfield H_(ua) in a structure including glasssubstrate/Ta(5)/Ni₈₁Fe₁₉(5)/Co₉₀Fe₁₀(1)/Cu(2.5)/Co₉₀Fe₁₀(3)/Mn₇₈Ir₂₂(8)/Ta(3)(filmthickness unit: nm). Annealing is conducted in a vacuum below 1×10⁻³ Pawhile applying a magnetic field of 240 kA/m in one direction and holdingtime is three hours. When the disordered MnIr film is used for theantiferromagnetic layer, a large H_(ua) is obtained immediately afterdeposition. The H_(ua) after the annealing is not found to be largelylowered than as deposited.

FIG. 6 shows temperature dependence of unidirectional magneticanisotropy provided by the MnPt film or MnIr film. The unidirectionalmagnetic anisotropy disappears at 350° C. for the MnPt film, and 250° C.for the MnIr film. Within the temperature range of 250 to 350° C., theunidirectional magnetic anisotropy is held only in the firstferromagnetic layer (fixing layer) exchange coupled to the MnPt film.

Using the following method, the magnetization direction of the firstferromagnetic layer (fixing layer) can be directed in the element heightdirection and the magnetization direction of the second ferromagneticlayer (free layer) can be directed in the track direction of themagnetic recording medium. The case of using the ordered MnPt film asthe first antiferromagnetic layer and the disordered MnIr film as thesecond antiferromagnetic layer will be explained here by way of example.While applying a magnetic field large enough to saturate themagnetization direction of the first ferromagnetic layer (fixing layer)in the element height direction, annealing is conducted at temperaturesof about 230 to 270° C. for several hours. This orders the MnPt filmwhich is in a disordered phase immediately after deposition into a CuAuIstructure and provides unidirectional magnetic anisotropy in the elementheight direction to the first ferromagnetic layer (fixing layer). Inthis case, the disordered MnIr film roughly directs, in the elementheight direction, the direction of unidirectional magnetic anisotropyprovided to the second ferromagnetic layer (free layer).

In a second annealing process, without changing the direction of theunidirectional magnetic anisotropy provided to the first ferromagneticlayer (fixing layer), the direction of the unidirectional magneticanisotropy provided to the second ferromagnetic layer (free layer) mustbe directed in the track direction of the magnetic recording medium.Specifically, while applying a magnetic field large enough to saturatethe magnetization direction of the second ferromagnetic layer (freelayer), annealing is conducted at a temperature of about 250° C. In thiscase, annealing time is sufficiently a short time below one hour. Adifference in the blocking temperature is used to adjust the annealingtemperature and time so that without changing the direction of theunidirectional magnetic anisotropy provided to the first ferromagneticlayer (fixing layer), the direction of the unidirectional magneticanisotropy provided to the second ferromagnetic layer (free layer) canbe directed in the track direction of the magnetic recording medium. Themagnetic anisotropy control of the second ferromagnetic layer (freelayer) is described here. The similar method for the magnetic flux guidemade of a soft magnetic film of NiFe can be used to control the magneticanisotropy.

The direction of the unidirectional magnetic anisotropy provided to thesecond ferromagnetic layer or the magnetic flux guide by the exchangecoupling to the second antiferromagnetic layer and the magnetostaticfield applied to the second ferromagnetic layer or the magnetic fluxguide from the hard magnetic film must be roughly matched. When thesedirections are matched, the magnetic energy is smallest and is stableand reading characteristic having high reliability can be obtained.

FIG. 7 shows simulation results of the micro track characteristic ofhead output in the case of using the prior art and the case of applyingthe present invention. A geometrical track width is 0.10 μm. There arecompared (1) the prior art hard biasing structure: longitudinal biasingratio of 5, (2) the prior art longitudinal biasing structure byinterface exchange coupling: exchange coupling field of 24 kA/m, and (3)this invention structure: longitudinal biasing ratio of 2+exchangecoupling field of 8 kA/m. In the prior art hard biasing structure of(1), the normalized signal output is very small. In other words, theinfluence of the insensitive zone formed by the hard magnetic filmarranged at the edge of the element is large so that the readingsensitivity is lowered over the track width. The prior art longitudinalbiasing structure by interface exchange coupling of (2) can obtain thelargest normalized signal output. The effective reading track widthdefined by the half-value width of the shown micro track profile iswide, which is not suitable for track width reduction. It is also foundthat the output is minimum near the head position: 0 μm. This suggeststhat the magnetization at the edge of the second ferromagnetic layer(free layer) is unstable. The sufficient longitudinal biasing effectcannot be expected. On the other hand, in this invention structure of(3), normalized signal output equal to that of the prior artlongitudinal biasing structure by interface exchange coupling of (2) canbe obtained, and an effective reading track width is not found to beincreased. Further, the unstable behavior of the magnetization at theedge of the element as seen in the prior art longitudinal biasingstructure by interface exchange coupling of (2) is not found. Thisinvention structure can satisfy all of high reading sensitivity,reduction of reading track width, and sufficient inhibition ofBarkhausen noise.

FIG. 8 shows simulation results of the micro track characteristic ofhead output in this invention structure when the exchange coupling fieldgiven by the antiferromagnetic layer is 4 kA/m and the magnetostaticfield (the parameter is the longitudinal biasing ratio) provided by thehard magnetic film is changed. For comparison, the results of the priorart hard biasing structure having a longitudinal biasing ratio of 5 arealso shown. A geometrical track width for these is 0.10 μm. In thisinvention structure, it is found that as the longitudinal biasing ratiois increased, the normalized signal output is decreased. In other words,this shows with increase of the longitudinal biasing ratio, theinfluence of the insensitive zone is larger and the reading sensitivityis decreased. In this invention structure, when the longitudinal biasingratio is larger than 4, large output increase cannot be expected ascompared with the prior art hard biasing structure. The longitudinalbiasing ratio is desirably below 4.

The exchange coupling field provided to the second ferromagnetic layer(free layer) by the antiferromagnetic layer largely changes thenormalized signal output and the longitudinal biasing effect. FIG. 9shows simulation results of the micro track characteristic of headoutput in this invention structure when the magnitude of themagnetostatic field provided by the hard magnetic film is fixed (thelongitudinal biasing ratio: 2) and the exchange coupling field providedby the antiferromagnetic layer is changed. A geometrical track width forthese is 0.10 μm. In this invention structure, it is found that as thelongitudinal biasing field is increased, the normalized signal output isdecreased. On the other hand, when the magnitude of the exchangecoupling field is reduced to 4 kA/m, the unstable behavior of themagnetization of the second ferromagnetic layer (free layer) as seen inthe longitudinal biasing structure by interface exchange coupling of (2)of FIG. 7 is not found. To realize high reading sensitivity, theexchange coupling field must be adjusted so as not to be too large.Since the magnetic field is roughly inversely proportion to the filmthickness of the second ferromagnetic layer (free layer), its magnitudecan be changed by the film thickness of the second ferromagnetic layer(free layer). When the film thickness is significantly large or small,it is not preferable since the resistive change rate is lowered and thesoft magnetic characteristic is deteriorated.

As shown in FIG. 5, the exchange coupling field given from Mn₇₈Ir₂₂(8nm) to Co₉₀Fe₁₀(3 nm) is about 30 kA/m. High reading sensitivity cannotbe obtained. To adjust the exchange coupling field provided to thesecond ferromagnetic layer (free layer), using the following method iseffective. A nonmagnetic layer for controlling the exchange couplingfield is introduced between the second ferromagnetic layer (free layer)and the second antiferromagnetic layer. For the nonmagnetic layer,candidates of effective materials are Cr, Cu, Ru, Rh, Ag, Pd, Re, Ir, Ptand Au. In place of the nonmagnetic layer, a ferromagnetic layer of NiFewith a material such as Nb added thereto can obtain the same effect. Inthe case of using such a ferromagnetic layer, the magnetization amountof the second ferromagnetic layer (free layer) and a ferromagnetic layerintroduced for controlling the exchange coupling field must not be toolarge.

An invention described in a further embodiment is a method forfabricating a magnetoresistive head including laminating a first and asecond ferromagnetic layers via a nonmagnetic conductive layer or anonmagnetic tunneling barrier layer; providing a first antiferromagneticlayer opposite to the nonmagnetic conductive layer or the nonmagnetictunneling barrier layer to form a magnetoresistive film; forming a pairof electrodes for flowing a sense current to the magnetoresistive film;arranging a second antiferromagnetic layer so as to provideunidirectional magnetic anisotropy to the second ferromagnetic layer;arranging a hard magnetic film so as to apply a magnetic field to thesecond ferromagnetic layer; arranging a magnetic flux guide for guidingan external magnetic field to the second antiferromagnetic layer; andarranging a third antiferromagnetic layer so as to provideunidirectional magnetic anisotropy to the magnetic flux guide, includinga process for finally deciding by the direction of a magnetic fieldapplied at annealing the direction of unidirectional magnetic anisotropyprovided to the first ferromagnetic layer by the first antiferromagneticlayer and the direction of unidirectional magnetic anisotropy providedto the second ferromagnetic layer or the magnetic flux guide by thesecond antiferromagnetic layer, wherein the process subjects the firstantiferromagnetic layer, the second antiferromagnetic layer or the thirdantiferromagnetic layer to annealing in the magnetic field underconditions of a temperature set from high to low in order of decreasingblocking temperature so as to provide the unidirectional magneticanisotropy.

The magnetoresistive head fabricated by the structure and fabricatingmethod as described above exhibits good reading characteristic and canbe mounted on a magnetic recording and reading device such as a magneticdisk unit and a magnetic tape device having a high surface recordingdensity.

As described above, the present invention can obtain a magnetoresistivehead which can provide both high reading sensitivity and low noise evenwhen the track width is being reduced. In other words, it can provide amagnetoresistive head which can achieve a high surface recording densityand is highly reliable without Barkhausen noise.

1.-9. (Canceled)
 10. Method for fabricating a magnetoresistive headcomprising: making a magnetoresistive element having a firstferromagnetic layer, a second magnetic layer, a nonmagnetic conductivelayer or a nonmagnetic tunneling barrier layer formed between said firstferromagnetic layer and said second ferromagnetic layer, a firstantiferromagnetic layer formed on the first ferromagnetic layer oppositeto the nonmagnetic conductive layer or a nonmagnetic tunneling barrierlayer, and a second antiferromagnetic layer formed on the secondferromagnetic layer opposite to the nonmagnetic conductive layer or anonmagnetic tunneling barrier layer, wherein a blocking temperatureT_(B1) of the first antiferromagnetic layer is higher than a blockingtemperature T_(B2) of the second antiferromagnetic layer, providingunidirectional magnetic anisotropy to the first ferromagnetic layer bythe first antiferromagnet6ic layer, by heating higher than T_(B2′) andapplying a magnetic field enough to saturate a magnetization directionof the first ferromagnetic layer in the element height direction,providing unidirectional magnetic anisotropy to the second ferromagneticlayer by the second antiferromagnetic layer, by heating lower thanT_(B2′) and applying a magnetic field enough to saturate a magnetizationdirection of the second ferromagnetic layer in the track width. 11.Method for fabricating a magnetoresistive head according to claim 10,wherein the magnetoresistive element has a hard magnetic film formed soas to provide a magnetic field to the second ferromagnetic layer. 12.Method for fabricating a magnetoresistive head according to claim 10,wherein the magnetoresistive element has a pair of electrodes forflowing a sense current to the magnetoresistive element.
 13. Method forfabricating a magnetoresistive head according to claim 10, wherein themagnetoresistive element has a flux guide for guiding an externalmagnetic field to the second ferromagnetic layer.
 14. Method forfabricating a magnetoresistive head according to claim 13, wherein themagnetoresistive element has a third antiferromagnetic layer arranged soas to provide unidirectional magnetic anisotropy to the magnetic fluxguide.
 15. Method for fabricating a magnetoresistive head according toclaim 14, wherein a blocking temperature of the third antiferromagneticlayer is T_(B3′) providing the unidirectional magnetic anisotropy to thefirst ferromagnetic layer, the second ferromagnetic layer and the thirdferromagnetic layer to annealing tin the magnetic field under conditionsof a temperature set from high to low in order of decreasing blockingtemperature.